Acids, bases and pHIB MYP Sciences: Subtopic test

1. 1
   Students at a school in Nairobi are sorting four household liquids using universal indicator solution. Lemon juice turned the indicator orange-red, tap water turned it green, a baking-soda solution turned it blue and oven cleaner turned it deep purple.

   (a)

   Which pH value is most likely for lemon juice?

   [1 mark]

   • ApH 3
   • BpH 7
   • CpH 10
   • DpH 14

   (b)

   Which of the four liquids is the most strongly alkaline?

   [1 mark]

   • ALemon juice
   • BTap water
   • CBaking-soda solution
   • DOven cleaner

   (c)

   Explain why universal indicator is more useful than litmus paper for comparing the lemon juice with a stronger acid.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A technician at a school in Lisbon is preparing to dilute a bottle of concentrated hydrochloric acid and a bottle of sodium hydroxide solution for a practical lesson. Both bottles carry the corrosive hazard symbol.

   (a)

   Which description of sodium hydroxide is correct?

   [1 mark]

   • AAn acid that turns litmus paper red
   • BA soluble base, called an alkali, that turns red litmus paper blue
   • CAn insoluble base that does not dissolve in water
   • DA neutral compound with a pH of 7

   (b)

   What does the corrosive hazard symbol warn about?

   [1 mark]

   • AThe substance will catch fire easily
   • BThe substance harms living things in the environment
   • CThe substance can damage skin, eyes and some metals
   • DThe substance may explode when heated

   (c)

   Suggest two safety precautions the technician should take when handling the concentrated solutions.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Priya, a student in Mumbai, wants to compare how well three brands of indigestion tablet (P, Q and R) neutralise acid. Each tablet contains a base. She crushes one tablet at a time, adds it to 50 cm³ of dilute hydrochloric acid containing universal indicator, stirs, and keeps adding tablets until the indicator turns green. She records the number of tablets needed. Brand P needed 3 tablets, brand Q needed 5 tablets and brand R needed 2 tablets. She did each test once and concludes that brand R is the best.

   (a)

   State a testable hypothesis for Priya's investigation, with a scientific reason, and identify the independent variable and the dependent variable.

   [3 marks]

   (b)

   Evaluate Priya's conclusion that brand R is the best, and suggest two improvements to her method.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A farming cooperative in Kerala finds that the soil in one of its fields has a pH of 4.5, which is too acidic for the crop it wants to grow. An agricultural adviser recommends spreading powdered lime (calcium hydroxide, a base) over the field. Some neighbours are worried about the cost and about rain washing lime into a nearby river.

   (a)

   Explain how adding lime changes the soil pH, and describe how the farmers could check the effect of the lime.

   [6 marks]

   (b)

   Discuss and evaluate the use of lime to treat the acidic soil.

   [6 marks]

   Total for question 4: 12 marks

End of questions